A short and efficient route from tetrahydrothiophene to thieno[2,3-d][1,3,2]dithiazolium salts

A synthesis of thieno2,3-d]1,3,2]dithiazolium salts from commercial tetrahydrothiophene has been developed. The reaction of thieno2,3-f]1,2,3,4,5]pentathiepin with LiAlH₄ in THF at −15 °C, after treatment with acetyl chloride, led to 2,3-(bisacetylthio)thiophene in high yield. Bis(acetylthio)thiophene reacted with sulfuryl chloride and then trimethylsilyl azide was added to afford a 1,3,2-dithiazolium chloride which was converted into a soluble tetrafluoroborate. Electrolytic reduction under controlled potential yielded a thieno2,3-d]1,3,2]dithiazolyl radical which was characterized by EPR in frozen methylene dichloride.